Impact of surface roughness and crusting on particle size distribution of edge-of-field sediments

The impact of field surface conditions and erosion processes on runoff volume, soil loss and sediment particle size during the rainfall runoff period was investigated. Results are reported for multiple events and from within individual events (intra-event) for sites with different corn (Zea mays L.) management systems (i.e., grain (CG), silage (CS), and silage-manure (CSM)). The multi-event bulk runoff volume and soil loss for CG were less than that for CS and CSM due to higher residue levels increasing surface roughness, ponding and infiltration. The aggregate stability for CG treatment was greater than that for CS and CSM and aggregate size peaks were identified at 5.4, 32,160 and 570 pm. Size peaks at 32 and 570 pm had the highest combined frequency (64%). Intra-event continuous monitoring covered silage plots with crop-rows oriented up-and-down the slope (CS) and along the contour (CScont). The crop-row orientation significantly influenced both runoff and sediment loss (concentration, load, size-distribution) patterns. The runoff volume and sediment concentration for CS was twice that of CScont. While no treatment difference attributable to residue coverage was evident for particle-size dynamics, crop-row orientation had a significant effect with finer-sized particles exported from the contoured site. Surface sealing, more pronounced at the silage sites, occurred after the 1st major storm in a season for all monitoring periods, types, and treatments, and it significantly influenced runoff generation, sediment load, and size distribution characteristics. Under crusted conditions, a storm with slightly higher rainfall depth but significant lower erosive potential, generated 53% more runoff and twice as much sediment compared to an early-season event. During crust development finer particles dominated sediment composition, later shifting to larger particles due to rill erosion once a stable crust was established. These results are expected to improve our understanding and, hence, predictive capability for transport of particulate-bound contaminants from row-crop systems, especially under conditions promoting surface crust formation. (c) 2008 Elsevier B.V. All rights reserved.